While acknowledging the difficulty of his task, in this book William Rosen sets out to examine why, after its immense success, the Roman empire fragmented into so many pieces. He argues that the bubonic plague was one of the key factors in the dissolution of the empire, since the resultant loss of population also meant a loss of soldiers and farmers. So he explores the reign of Justinian, who ruled the empire when plague first broke out in 540 CE. This is an impressively wide-ranging book covering epidemiology, medical history, economics, agricultural history, evolution, and architecture.